1. Field of the Invention
The invention relates to a transparent conductive film having transparency in the visible light region and including a film substrate and a transparent conductive laminate that is provided on the film substrate and includes at least two transparent conductive layers. The invention also relates to a touch panel having such a transparent conductive film. The transparent conductive film of the invention is used for transparent electrodes in touch panels or displays such as liquid crystal displays and electroluminescence displays and also used for electromagnetic wave shielding or prevention of static buildup on transparent products. According to position detection method, touch panels may be classified into optical, ultrasonic, capacitance, and resistive touch panels. The transparent conductive film of the invention is suitable for use in capacitance touch panels, specifically, projection-type capacitance touch panels.
2. Description of the Related Art
Concerning a conventional transparent conductive film, the so-called conductive glass is well known, which includes a glass substrate and a transparent conductive layer of indium oxide formed thereon. Unfortunately, it has low flexibility or workability and cannot be used in some applications because the substrate is made of glass.
In recent years, therefore, various plastic films including polyethylene terephthalate films have been used to form substrates because of their advantages such as good impact resistance and light weight as well as flexibility and workability, and there has been used a transparent conductive film including a transparent conductive layer of indium oxide formed on such substrates.
Such a transparent conductive layer is often crystallized to meet requirements such as low resistance, high transmittance, and high durability. The crystallization method generally includes forming an amorphous transparent conductive layer on a film substrate and then crystallizing the amorphous transparent conductive layer by heating or any other method. Unfortunately, when such a transparent conductive film is produced, it is generally difficult to heat the film substrate to 200° C. or higher during the crystallization, depending on the heat resistance of the film substrate. Thus, there is a problem in which the time required to crystallize the transparent conductive layer is longer in the case where the transparent conductive film is produced with a film substrate than in the case where the transparent conductive layer is formed on a glass substrate and crystallized by heating at high temperature.
To solve the crystallization time problem and to satisfy reliability at high temperature and high humidity, it is proposed that transparent conductive layers having a two-layer structure should be formed on a film substrate. For example, it is proposed that a thin film of an indium-tin complex oxide with a low tin oxide content should be formed on the film substrate side and another thin film of an indium-tin complex oxide with a high tin oxide content should be formed thereon (JP-A 2006-244771).